W5 - Colour

Question 1

What is properties of colour

Answer 1

• Interpretation of the brain

- Context-specific

Question 2

What did Issac Newton found in colour

Answer 2

White light is made up up of all visible

Question 3

What did Young and Helmholtz found in colour

Answer 3

3 receptors - Trichromacy

Question 4

What did Edwalrd Hering sugest

Answer 4

Opponency: Red-Green; Blue-Yellow. First stage: trichromatic; Opponent stage

Question 5

Define neural substrate

Answer 5

Indicate a part of the nervous system underlying a behaviour or physiological state

Question 6

Kraukskopf (1982): Aims, Method & Stimuli

Answer 6

Aims: Simple colour detection (Presence or Absense binary)

• Small disc whose colour varied in time along an axis of opponent colour space
• Participants indicated whether a test pulse was visible before/after prolonged exposure to a stimulus modulated along given axis
• Contrast/visibility of pulse varied until “threshold” reached (75% correct)

Question 7

What is a colour space

Answer 7

Method by which a light and colour may be represented such that its definition is unique and replicable

Question 8

What are the 3 cones.

Answer 8

L Cones: Reds
M Cones: Green
S Cones:: Blue

Question 9

What is the cardinal colour space

Answer 9

2 Chromatic Axes (Colour): R-G; B-Y

1 Achromatic Axis: Luminance

Question 10

What is the cone’s relationship to the cardinal colour space

Answer 10

L+M = Bluish Yellowishness (Luminance)
L-M = Reddish Greenishness
S - (L+M) = Blackish Whitishness

Question 11

Kraukskopf (1982): Results

Answer 11

Distance from centre = Adapted - Unadapted Threshold

Bigger difference from centre = More adaptation effect

Question 12

Kraukskopf (1982): Results Interpretation

Answer 12

2 Chromatic and 1 Acrhomatic Axis = Opponency

1. ) Each axis shows independent adaptability
   - Threshold only raised by adapting to a stimulus along the same axis (unaffected by adaptation to other axes)

2.) Orthogonality: 3 independent detection mechanisms mediate the transmission of spatio-chromatic information from retina to cortex

Question 13

In psychophysics, who are the subjects

Answer 13

Neurons.

Question 14

What are cardinal neurons

Answer 14

Group of neurons involved in colour vision

Question 15

What are properties of cardinal neurons

Answer 15

1. ) Chromatic sensitivity clustered along cardinal axes (RG/BY/BW): To get pattern of independent adaptability
2. ) Change in output after prolonged exposure

Question 16

How does the visual system work

Answer 16

Photoreceptors > Bipolar > Retinal Ganglion Cell (Difference in sensitivity) > LGN > Cortex

Question 17

LGN and Cortex connections

Answer 17

More V1 to LGN than LGN to V1

Question 18

What are cells in the layers of the LGN

Answer 18

1. ) Parvo Cellulular: Small (Retinal P cells)
2. ) Konio Cellulular: Medium
3. ) Magno Cellular: Big (Retinal M cells)

Question 19

Derrington (1984): Aim

Answer 19

Are the 3 LGN cells grouped along in cardinal axis?

Question 20

Derrington (1984): Stimuli and Methods

Answer 20

Macaque LGN neuron

• Receptive field locations established with coloured spot stimuli (see how output of neuron change as a function of colour and luminance properties as in opponent space)
• Stimuli modulated until a minimum “null response” is found. Silent substitution method.

Question 21

What is the silent substitution method in Derington (1984)

Answer 21

Two coloured light exchange with no effect on output of neurons (If Red switch to Blue and no effect = neurons inresponsive and orthogona axisl)

Question 22

Derrington (1984): Results

Answer 22

Neurons “chromatic signature” fell into 3 subgroups.

1.) Parvo Cellular: Less sensitive to luminance; Specific senstivity to either RG or BY
> Hence, only this gives a true sense of colour

2. ) Konio Cellulular: Not sure. But they have a large number of S cones (maybe augment)
3. ) Magno Cellular: Very sensitive to luminance; Weak colour sensitivity.

Question 23

Can Derington’s (1984) study explain cardinal properties

Answer 23

Not fully. The neurons did not change output after prolonged exposure (adaptation). Only established chromatic signature.

Question 24

Krauskopf (1990) Aim

Answer 24

Replicate Derington (1984) in the cortex

Question 25

Krauskopf (1990) Results

Answer 25

• In none of each cortical group, there is no clustering. Neurons redistributed across colour plane along the cortex.
• Showed strong adaptation effect & selectivity. Reduce output after prolonged exposure.

Question 26

LGN vs V1

Answer 26

LGN: Cardinal colour signature but no adaptation
V1: No cardinal colour signature but adapt

Question 27

What does all the findings suggest in colour and cardinal behaviour. What does it imply?

Answer 27

LGN (Chromatic Signature) + V1 (Adaptation) = Detection of presence.

• There is no modulation of colour. There is no “cardinal neurons” doing “cardinal behaviour”.